Conventionally, water containing caustic alkali rather than pure water is used in water electrolysis to produce pure hydrogen and oxygen because pure water does not have satisfactorily high electrical resistance. But the aqueous alkaline solution may corrode the electrolyte cell or may form a gas contaminated by alkaline gas.
A method has been proposed for electrolyzing pure water in an electrolytic apparatus which uses a solid polymeric electrolyte made of a cation exchange membrane having anodic and cathodic-catalysts bonded to opposite sides (see, for example, U.S. Pat. No. 4,039,409. Since the cation exchange resin used in this method must have high ion conductivity, strong bond to anodic and cathodic catalysts, high heat resistance, great resistance to oxidation and low gas permeability, the use of a perfluorocarbon cation exchange membrane having good chemical and heat resistance properties has been considered necessary. The most famous perfluorocarbon cation exchange membrane is "NAFLON" which is a trade name for a perfluorosulfonated membrane sold by Du Pont. This membrane is manufactured as a copolymer of tetrafluoroethylene and a sulfonyl-containing monomer capable of introducing an ion exchange group. But the conventional cation exchange membrane is not very much used in commercial electrolysis of pure water since it involves complex polymerization procedure and is costly.